The present invention relates to a cellular mobile telephone system and method, and more particularly to a modular system in which the control functions are largely distributed to the cell stations associated with the individual cells or zones which comprise a service area.
Cellular mobile telephone systems are well known. Such systems use a plurality of cell stations for broadcasting paging signals to and maintaining voice communications with the mobile telephone units within the cell. Control of telephone call routing, channel assignment and the RF communications are typically controlled by a central control station.
The installation of such systems requires an initial installation of control and switching equipment at the central control station having the capacity anticipated for ultimate user saturation of the geographic area. The capital expenditures required for such equipment is often prohibitive where the initial number of subscribers cannot be expected to approach maximum anticipated user density.
An additional problem with generally known systems is the redundancy of the equipment at the central control station necessary to ensure continuous system operation in the event of malfunction, etc. Without duplication of this massive capacity and the accompanying expense, the danger of interrupted service is very real.
Another problem with some known systems is the need to connect the communication channels in all cells to a single central control station. For cells which are relatively distant from the central control station, the costs of such connections can be relatively high.
It is often of some importance that single component failures within a mobile telephone system not be permitted to cause loss of the entire system or a large portion thereof. One method of avoiding such a loss is to duplicate all elements of the system; however the cost of entire sysetm duplication may be prohibitive.
Because service from a mobile telephone is usually not a necessity and sale of the service is often quite competitive, a mobile telephone system should seldomly be unavailable and unusable communication paths should be avoided. However, some known mobile telephone system have no or limited means to provide for the early detection of component failures and to isolate the failures to modules which can be readily replaced.
These and many other problems of generally known systems are obviated by the modular approach of the present invention and the distribution of many of the control funcitons from the central control station to the cell stations. Duplication of reduced capacity central control station equipment is financially feasible and the dynamic assignment of identical radio interface modules associated with each duplex radio channel for paging, monitoring and voice communication functions provides both security from interrupted service and significantly reduced costs.
More importantly, the modular approach of the present invention permits initial system operation with a capacity commensurate with the minimum number of subscribers expected, and infinite expansion to meet changing system requirements without obsolescence. Additionally, the approach of the present invention provides for automated tests of various system components and additional tests which can be executed on demand to assist in isolating component failures. Selective duplication and cross-coupling of certain components reduces the impact of many types of component failures.
These and many other objects and advantages of the present invention will be apparent from the claims and from the detailed description of a preferred embodiment when read in conjunction with the appended drawings.